Weight sensing device

ABSTRACT

A device for indicating the weight of an object is disclosed herein and includes a first circuit for producing an oscillatory excitation signal which is capacitively coupled to a second circuit for producing at the output of said second circuit a signal indicative of the weight of said object. In this regard, the second circuit is capacitively coupled to the first circuit by a coupling plate mounted to a support member for movement in response to the weight of said object. This output signal is applied to an electromagnetic assembly which, in response thereto, applies to said coupling plate a proportional force which is equal and opposite to the gravitational force of the supported object for terminating movement of said coupling plate. In this manner, the output signal may be monitored for indicating the weight of said object.

United States Patent Zimmerer [54] WEIGHT SENSING DEVICE [72] Inventor:Robert W. Zimmerer, Boulder,

[73] Assignee: Scientech, Inc., Boulder, C010.

[22] Filed: Nov. 10, 1971 [211 App]. No.: 197,336

[52] US. Cl. ..177/210, 177/212 [51] Int. Cl. ....G0lg 3/08, G01g 7/06,G0lg 7/02 [58] Field of Search ..177/210, 212,1,164

[56] References Cited UNITED STATES PATENTS 2,597,831 5/1952 Willis..177/164 3,078,936 2/1963 Thomson ..177/210 3 ,1 33,606 5/1964 Thomson177/210 3,172,493 3/1965 Von Koch et al ..177/210 3,519,095 7/1970 Tomes..177/212 3,604,525 9/1971 Blethen et al 177/212 FOREIGN PATENTS ORAPPLICATIONS 1,159,197 2/1958 France ..177/210 [151 3,680,650 [451 Aug.1,1972

736,006 8/1955 GreatBritain ..177/210 919,771 2/1963 GreatBritain..177/210 Primary Examiner-Robert S. Ward, Jr. Attorney-Stephen C. Shear[5 7] ABSTRACT A device for indicating the weight of an object isdisclosed herein and includes a first circuit for producing anoscillatory excitation signal which is capacitively coupled to a secondcircuit for producing at the output of said second circuit a signalindicative of the weight of said object. In this regard, the secondcircuit is capacitively coupled to the first circuit by a coupling platemounted to a support member for movement in response to the weight ofsaid object. This output signal is applied to an electromagneticassembly which, in response thereto, applies to said coupling plate aproportional force which is equal and opposite to the gravitationalforce of the supported object for terminating movement of said couplingplate. In this manner, the output signal may be monitored for indicatingthe weight of said object.

9 Claims, 2 Drawing Figures PATENTEDMJP H972 INVENTOR. ROBERT W.ZIMMERER BACKGROUND OF THE INVENTION 1 Field of the Invention Thepresent invention relates generally to balancing devices and moreparticularly to an electromagnetic device for measuring the weight of anobject.

2. Description of the Prior Art The necessity for detennining the weightof small lightweight articles, even minute particles, is readilyapparent. This is particularly evident in, for example, the field ofpharmacology where grams of ingredients are necessarily mixed togetherin exact proportions. Heretofore, there have been many balancing devicesfor making such measurements such as, for example, the electromechanicaltype or the strictly mechanical type, both of which have been found tobe somewhat inaccurate in making small measurements and, therefore, notcompletely satisfactory for their intended use.

More recently, capacitance responsive devices have been suggested buthave been found to be complicated, both from a structural standpoint andan electrical standpoint. In addition, many of these more recent devicesutilize sinusoidal and similar operating signals which produce furtherproblems such as, for example, harmonic and phase shift distortion, aswell as requiring additional and more complicated circuit components.

SUMMARY OF THE INVENTION The present invention, which provides aheretofore unavailable improvement over previous balancing devices,comprises a device for indicating the weight of an object in anaccurate, reliable and uncomplicated manner. The device, in response tothe weight of an object, capacitively couples an excitation signal,preferably-a square wave signal, from a first circuit to a secondcircuit for producing an output signal having a characteristicindicative of the weight of the object under consideration.

Accordingly, an object of the present invention is to provide a new andimproved device for measuring the weight of an object, especiallyobjects weighing, for example, one gram and less.

Another object of the present invention is to provide a new and improvedweight measuring device which is accurate and reliable in operation,uncomplicated in construction and economical to manufacture.

Yet another object of the present invention is to provide a new andimproved weight measuring device which eliminates quadrature distortionsuch as, for example, harmonic and phase shift distortion and which maybe adapted for use with a simple and economical excitation source.

Still another object of the present invention is to provide a device ofthe last-mentioned type utilizing a square wave excitation signal and acapacitance coupling principle for producing an electrical signalindicative of the weight of an object.

Yet another object of the present invention is to provide a new andimproved device which minimizes the number of components required forindicating the weight of an object.

Still another object of the present invention is to provide a new andimproved weight indicating device which utilizes a capacitance couplingprinciple and an uncomplicated capacitance coupling arrangement forcarrying out said principle.

A further object of the present invention is to provide a new andimproved weight indicating assembly which capacitively couples anexcitation signal from a first circuit having a pair of capacitor platesto a second circuit having a pair of capacitor plates for producing aweight indicative signal at a single junction connected directly to saidsecond-mentioned capacitor plates.

These and other objects and features of the present invention willbecome apparent from the following descriptions.

BRIEF DESCRIPTION OF THE DRAWING In the Drawing FIG. 1 is a partialschematic diagram and partial perspective view of a weight sensingdevice constructed in accordance with the present invention; and

FIG. 2 is a schematic diagram of the electrical circuitry utilized withthe device of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION Turning now to the drawing,wherein like components are designated by like reference numeralsthroughout the various figures, a device for determining and indicatingthe weight of an object is illustrated in FIG. 1 and is generallydesignated by the reference numeral 10. As will be described in moredetail hereinafter, device 10, utilizing preferably a square waveexcitation signal and a capacitance coupling principle, produces a DCcurrent in response to the weight of an object under consideration. ThisDC current is applied to an electromagnetic arrangement for producing alinearly proportional electromagnetic force equal in magnitude andopposite in direction to the gravitational force of the object. In thismanner, the DC current can be measured by an appropriately calibratedmeter for designating, for example, within one milligram, the weight ofthe object under consideration.

As illustrated in FIG. 1, device 10 includes an object support assembly12 having a vertically extending, preferably dielectric, post 14 and abalance pan l6 centrally mounted to the top end of the post. A pluralityof leaf springs or other suitable means 18 are provided for mountingpost 14 to a stationary support generally designated by the referencenumeral 20 so that the post is capable of moving in an axial directionbut is prevented from moving in any other direction. Accordingly, whenan object 22, the object under consideration, is placed on balance pan16, post 14 moves axially downward in response to the gravitationalforce F g applied to the post by the object.

A first pair of horizontally extending and vertically spacedelectrically conductive capacitor plates 24a, 24b and a second pair ofhorizontally extending and equally vertically spaced electricallyconductive capacitor plates 26a, 26b are positioned on opposite sides ofpost 14 and in horizontal alignment with each other. The capacitorplates, which are mounted in these positions to stationary support 20and electrically insulated therefrom by suitable dielectric fasteningmeans 28, comprise an important part of a circuit arrangement 30responsible for providing the aforedescribed DC current (designated I,,)in response to the weight of object 22.

An equally important part of circuit arrangement 30 is a horizontallyextending and electrically conductive capacitance coupling plate 32which is centrally mounted to post 14 for movement therewith and whichextends outward so as to be between capacitor plates 24a and 24b on oneend and capacitor plates 26a and 26b on the opposite end. As illustratedin FIG. 1, coupling plate 32 is physically connected only with post 14which, of course, results in a rather uncomplicated mechanical structureand, therefore, a more economical device.

Operationally, with no object supported on balance pan 16, that is, withonly the tare weight of support assembly l2, coupling plate 32 iscentrally positioned between upper capacitor plates 24a, 26a and lowercapacitor plates 24b, 26b. In this position, circuit arrangement 30produces no output current I, and, therefore, indicates zero weight onbalance pan 16, that is, the tare weight of the device. Upon placing anobject 22 on the balance pan, post 14 and coupling plate 32 movedownward causing the latter to change its position relative to thecapacitor plates. This, in turn, causes circuit arrangement 30 toproduce output current I which is dependent upon and proportional to,both in magnitude and polarity, the position of the coupling platerelative to the capacitor plates.

Output current 1,, which increases as coupling plate 32 moves closer toplates 24b and 26b, is applied to a coil 34 and thereafter to anappropriately calibrated meter 36. Coil 34 is positioned around adielectric core 37 which, in turn, is mounted to the lower end of post14 around an iron slug 39. A permanent magnet such as, for example, apot magnet 38 displaying radial symmetry and a radial magnetic field issuitably mounted under slug 39 and enclosed by an iron casing 41, asillustrated in both FIGS. 1 and 2. In this manner, current I, and themagnetic field of magnet 38 cooperate to produce an axially upwardelectromagnetic force Fe on post 14, the force being linearlyproportional to current 1,. As the weight of object 22 moves couplingplate 32 closer to plates 24b and 26b, the current I, increases, causingthe electromagnetic force to increase linearly therewith. When theforces Fg and Fe come into equalibrium, the downward motion of plate 32terminates. This, of course, means that the current 1,, which islinearly proportional to Fe, is, at this time, linearly proportional toFg and, therefore, the weight of object 22. Accordingly, by measuringthis current with appropriately calibrated meter 36, the weight ofobject 22 can be determined.

Turning to FIG. 2, attention is now directed to the details of circuitarrangement 30 which, as stated above, include capacitor plates 24a, 24band 26a, 26b, as well as capacitance coupling plate 32. As illustrated,capacitor plates 24a and 24b are respectively connected to oppositesides of an oscillatory signal producing source 42, which, inconjunction with the capacitor plates, comprise a first or excitationcircuit 44. On the other hand, capacitor plates 26a and 26b arerespectively connected to an output junction 46 so as to form a secondor output circuit 48.

Operationally, in response to an oscillatory excitation signal 50,provided by source 42, circuit 44 produces across plates 24a and 24b asimilarly shaped signal which is capacitively coupled to circuit 48 bymovable or floating plate 32, if the latter is off center, that is,closer to the lower capacitor plates than the upper capacitor plates, orvice versa. Assuming for the moment that the coupling plate is closer tocapacitor plates 24b and 26b, due to the weight of object 22, circuit48, in response to the coupled signal, produces at output junction 46 asimilarly shaped signal 52, displaying a frequency equal to that ofexcitation signal 50 and an amplitude dependent upon and proportional tothe distance in which plate 32 is off center. As will be seenhereinafter, this signal is initially responsible for producing theaforedescribed DC current I.,.

On the other hand, if coupling plate 32 is on center or equidistant fromthe upper and lower capacitor plates, which is the case when post 14 isin its equilibrium state, that is, when the post is not supporting an object, the signal on plate 32 averages to zero. This, in turn, eliminatesany production of a signal at the output junction 46 of circuit 48 and,accordingly, eliminates any production of DC current 1,.

Attention is directed back to oscillatory signal producing source 42,which, in accordance with the present invention, preferably comprises amultivibrator circuit or other similar simple and economical generatorfor providing a square wave or nearly square wave excitation signal 50which, in turn, causes a square wave output signal 52 to be produced atjunction 46. In addition to taking advantage of a simple and economicalgenerator, the utilization of a square wave excitation signal eliminatesharmonic distortion and phase shift distortion as well as other similarquadrature distortion otherwise caused by the use of, for example, asinusoidal signal which, heretofore, has been suggested for excitingcapacitor coupled weighing devices. In this regard, it should be readilyapparent that distortion of the type described, if present, couldadversely affect the accuracy of a weighing device in a substantial way,especially where the device is provided for weighing lightweightarticles of, for example, one gram or less. In addition, by utilizing asquare wave signal, more of the signal is available for determining theweight of an object than is the case when utilizing a sinusoidal signal.This is due to the fact that output signal 52, as will be seenhereinafter, is processed for producing a signal which is proportionalto the area of the wave form and clearly a sine wave has less such areathan a square wave and, thus, does not produce as accurate aproportional signal as a square wave. Other advantages in utilizing asquare wave excitation signal will become apparent'hereinafter.

Turning now to the remainder of the circuitry making up device 10,attention is firstly directed to a synchronous switch arrangement 54provided for converting the output signal 52 into a DC signal 56, theamplitude of which is proportional to the peak-to-peak value of signal52. In this regard, arrangement 54 includes a capacitor 58 and a switch60 connected at one end to a junction point 62 so that its otherwisefree end switches between a pair of junctions 64 and 66. As illustratedin FIG. 2, the switch is connected with signal producing source 42, asdiagrammatically shown by dotted line 68, and is responsive toexcitation signal 50 for switching between junctions 64 and 66 insynchronism with the excitation signal, that is, at a frequency equal toand in phase with the excitation signal. In this manner, the capacitor58, in response to output signal 52, oscillates between a charging stateand a discharging state in synchronism with excitation signal 50 forproducing DC signal 56. It should be noted that by utilizing a squarewave excitation signal the switch 60 can be directly driven betweenjunctions 64 and 66 by signal producing source 42 without the necessityof providing an additional square wave producing device.

It should be apparent from the foregoing that synchronous switch 54provides the proper polarity to device 10. Specifically, when plate 32is below center, the signal 56 is, for example, positive, causing I, tobe, for example, positive, so as to produce an upwardly directed forceFe. On the other hand, if plate 32 is above center, signal 56 would beof opposite polarity, that is, negative, causing a negative I and adownwardly directed force Fg. In this manner, the object 22 can beweighed in the manner illustrated, as well as by inverting device andsupporting object 22 on the opposite side of balance pan 16.

The DC signal 56 is amplified by a conventional operational amplifiercircuit, generally designated by the reference numeral 72, andthereafter applied to the base of a transistor 74 which has itscollector connected with a volt DC supply and its emitter connected toone end of coil 34. The transistor, in response to the amplified signalapplied to its base and the +20 volt supply, provides the aforedescribedDC current I which is applied to coil 34 for ultimately producingelectromagnetic force Fe.

As illustrated in FIG. 2, meter is connected to the otherwise free endof coil 34 for receiving and measuring DC current In this regard, themeter may be appropriately calibrated to measure the weight of object 22directly in an accurate and uncomplicated manner.

Although one embodiment of the present invention has been illustratedand described, it is anticipated that various changes and modificationswill be apparent to those skilled in the art and that such changes maybe made without departing from the scope of the invention, as defined bythe following claims.

What is claimed is:

l. A device for sensing the weight of an object, comprising: a firstcircuit including a pair of confronting and spaced-apart electricallyconductive members, said circuit being adapted for connection with asignal producing source for producing an oscillatory excitation signalacross said electrically conductive members; a second circuit includinga junction and a pair of con fronting and spaced-apart electricallyconductive members connected directly to said junction, saidsecondmentioned members being spaced from said first-mentioned members;support means adapted to support said object; an electrically conductivecoupling member including a first portion positioned between saidfirst-mentioned members and a second portion positioned between saidsecond-mentioned members for capacitively coupling said second circuitto said first circuit, said coupling member being mounted with saidsupport means for movement relative to said first and second-mentionedmembers in response to the weight of said object when the latter issupported by said support means, said second circuit in response to saidexcitation signal producing at said junction an oscillatory outputsignal the amplitude of which is proportional to the position of saidcoupling member and, therefore, indicative of the weight of said object.

2. A device according to claim 1 wherein said oscillatory excitationsignal is substantially a square wave signal.

3. A device according to claim 1 wherein said output signal oscillatesabout a central reference value indicative of substantially zero weightsupport by said support means.

4. A device according to claim 1 including means connected with saidsecond circuit and operationally connected with said coupling member forapplying a force to said coupling member in response to said outputsignal, said force being equal and opposite to the gravitational forceof said object for terminating movement of said coupling member.

5. A device for sensing the weight of an object, comprising: a firstcircuit including a first pair of confronting and spaced-apartelectrically conductive members, said circuit being adapted forconnection with a signal producing source for producing a substantiallysquare wave excitation signal across said first pair of members; asecond circuit including a second pair of confronting and spaced-apartelectrically conductive members and a single junction connected to saidsecond members, said second members being in alignment with and spacedfrom said first members; support means adapted to support said object;an electrically conductive coupling member including a first portionpositioned between said first members and a second portion positionedbetween said second members for capacitively coupling said secondcircuit to said first circuit, said coupling member being electricallyinsulated from and mounted to said support means for movement relativeto said first and second pairs of members in response to the weight ofsaid object when the latter is supported by said support means, saidsecond circuit in response to said excitation signal producing at saidjunction a square wave output signal, the peak-to-peak amplitude ofwhich is proportional to the position of said coupling member; a thirdcircuit connected with the junction of said second circuit and includingmeans for converting said square wave output signal into a directcurrent signal having a magnitude proportional to the peak-topeakamplitude of said output signal, said third circuit further includingmeans responsive to said direct current signal for producing a current,the magnitude of which is proportional to the magnitude of said directcurrent signal; and means connected with said lastmentioned means andoperationally connected with said coupling member for applying a forceto the latter in response to and proportional to said current, saidforce being equal and opposite to the gravitational force of said objectfor terminating movement of said coupling member whereby the magnitudeof said current producing said equal and opposite force is linearlyproportional to the weight of said object.

6. A device for sensing the weight of an object, said device comprising:a first circuit adapted for connection with a signal producing sourcefor producing a square wave excitation signal; a second circuit spacedfrom said first circuit and including an output junction; support meansadapted to support said object; coupling means mounted to said supportmeans for movement in response to the weight of said object, saidcoupling means capacitively coupling said excitation signal to saidsecond circuit for producing at said junction a square wave outputsignal having a peak-to-peak amplitude dependent upon the position ofsaid coupling means; means connected with said junction and responsiveto said output signal for producing a current, the magnitude of which isdependent upon the peak-to-peak amplitude of said output signal; andmeans connected with said last-mentioned means and operationallyconnected with said coupling means for applying a force to the latter inresponse to and proportional to said current, said force being equal andopposite to the gravitational force of said object for terminatingmovement of said coupling means whereby the magnitude of said currentproducing said equal and opposite force is linearly proportional to theweight of said object.

7. A device for sensing the weight of an object, comprising: a firstcircuit adapted for connection with a signalproducing source forproducing a square wave excitation signal; a second circuit spaced fromsaid first circuit and including an output junction; support meansadapted to support said object; coupling means mounted to said supportmeans for movement in response to the weight of said object, saidcoupling means capacitively coupling said excitation signal to saidsecond circuit for producing at said output junction a current having amagnitude dependent upon the position of said coupling means; and meansconnected with said junction and operationally connected with 'saidcoupling means for applying a force to the latter in response to andproportional to said current, said force being equal and opposite to thegravitational force of said object for terminating movement of saidcoupling means whereby the magnitude of said current producing saidequal and opposite force is proportional to the weight of said object.

8. A device for sensing the weight of an object, comprising: a firstcircuit including a pair of confronting and spaced-apart electricallyconductive members, said said second circuit to said first circuit, saidcoupling member being mounted to and physically connected solely withsaid support member for movement relative to said first andsecond-mentioned members in response to the weight of said object, saidsecond circuit in response to said excitation signal and the position ofsaid coupling member producing at said junction an output signal havinga characteristic proportional to the position of said coupling memberand, therefore, indicative of the weight of said object.

9. A device for sensing the weight of an object, comprising: a firstcircuit adapted for connection with a signal producing source forproducing an excitation signal; a second circuit spaced from said firstcircuit d includin an out t 'unction; a su rt member a pted to s upports aid object; a cougmig member capacitively coupling said second circuitto said first circuit, said coupling member being mounted to andphysically connected solely with said support member for movement inresponse to the weight of said object; said second circuit in responseto said excitation signal and the position of said coupling memberproducing at said junction an output signal having a characteristicproportional to the position of said coupling member and, therefore,indicative of the weight of said object.

1. A device for sensing the weight of an object, comprising: a firstcircuit including a pair of confronting and spaced-apart electricallyconductive members, said circuit being adapted for connection with asignal producing source for producing an oscillatory excitation signalacross said electrically conductive members; a second circuit includinga junction and a pair of confronting and spaced-apart electricallyconductive members connected directly to said junction, saidsecond-mentioned members being spaced from said first-mentioned members;support means adapted to support said object; an electrically conductivecoupling member including a first portion positioned between saidfirst-mentioned members and a second portion positioned between saidsecond-mentioned members for capacitively coupling said second circuitto said first circuit, said coupling member being mounted with saidsupport means for movement relative to said first and second-mentionedmembers in response to the weight of said object when the latter issupported by said support means, said second circuit in response to saidexcitation signal producing at said junction an oscillatory outputsignal the amplitude of which is proportional to the position of saidcoupling member and, therefore, indicative of the weight of said object.2. A device according to claim 1 wherein said oscillatory excitationsignal is substantially a square wave signal.
 3. A device according toclaim 1 wherein said output signal oscillates about a central referencevalue indicative of substantially zero weight support by said supportmeans.
 4. A device according to claim 1 including means connected withsaid second circuit and operationally connected with said couplingmember for applying a force to said coupling member in response to saidoutput signal, said force being equal and opposite to the gravitationalforce of said object for terminating movement of said coupling member.5. A device for sensing the weight of an object, comprising: a firstcircuit including a first pair of confronting and spaced-apartelectrically conductive members, said circuit being adapted forconnection with a signal producing source for producing a substantiallysquare wave excitation signal across said first pair of members; asecond circuit including a second pair of confronting and spaced-apartelectrically conductive members and a single junction connected to saidsecond members, said second members being in alignment with and spacedfrom said first members; support means adapted to support said object;an electrically conductive coupling member including a first portionpositioned between said first members and a second portion positionedbetween said second members for capacitively coupling said secondcircuit to said first circuit, said coupling member beiNg electricallyinsulated from and mounted to said support means for movement relativeto said first and second pairs of members in response to the weight ofsaid object when the latter is supported by said support means, saidsecond circuit in response to said excitation signal producing at saidjunction a square wave output signal, the peak-to-peak amplitude ofwhich is proportional to the position of said coupling member; a thirdcircuit connected with the junction of said second circuit and includingmeans for converting said square wave output signal into a directcurrent signal having a magnitude proportional to the peak-to-peakamplitude of said output signal, said third circuit further includingmeans responsive to said direct current signal for producing a current,the magnitude of which is proportional to the magnitude of said directcurrent signal; and means connected with said last-mentioned means andoperationally connected with said coupling member for applying a forceto the latter in response to and proportional to said current, saidforce being equal and opposite to the gravitational force of said objectfor terminating movement of said coupling member whereby the magnitudeof said current producing said equal and opposite force is linearlyproportional to the weight of said object.
 6. A device for sensing theweight of an object, said device comprising: a first circuit adapted forconnection with a signal producing source for producing a square waveexcitation signal; a second circuit spaced from said first circuit andincluding an output junction; support means adapted to support saidobject; coupling means mounted to said support means for movement inresponse to the weight of said object, said coupling means capacitivelycoupling said excitation signal to said second circuit for producing atsaid junction a square wave output signal having a peak-to-peakamplitude dependent upon the position of said coupling means; meansconnected with said junction and responsive to said output signal forproducing a current, the magnitude of which is dependent upon thepeak-to-peak amplitude of said output signal; and means connected withsaid last-mentioned means and operationally connected with said couplingmeans for applying a force to the latter in response to and proportionalto said current, said force being equal and opposite to thegravitational force of said object for terminating movement of saidcoupling means whereby the magnitude of said current producing saidequal and opposite force is linearly proportional to the weight of saidobject.
 7. A device for sensing the weight of an object, comprising: afirst circuit adapted for connection with a signal producing source forproducing a square wave excitation signal; a second circuit spaced fromsaid first circuit and including an output junction; support meansadapted to support said object; coupling means mounted to said supportmeans for movement in response to the weight of said object, saidcoupling means capacitively coupling said excitation signal to saidsecond circuit for producing at said output junction a current having amagnitude dependent upon the position of said coupling means; and meansconnected with said junction and operationally connected with saidcoupling means for applying a force to the latter in response to andproportional to said current, said force being equal and opposite to thegravitational force of said object for terminating movement of saidcoupling means whereby the magnitude of said current producing saidequal and opposite force is proportional to the weight of said object.8. A device for sensing the weight of an object, comprising: a firstcircuit including a pair of confronting and spaced-apart electricallyconductive members, said circuit being adapted for connection with asignal producing source for producing an excitation signal across saidelectrically conductive members; a second circuit including a junctionand a pair of confronting and spaced-apart eleCtrically conductivemembers connected with said junction, said second-mentioned membersbeing spaced from said first-mentioned members; a support member adaptedto support said object; an electrically conductive coupling memberincluding a first portion positioned between said first-mentionedmembers and a second portion positioned between said second-mentionedmembers for capacitively coupling said second circuit to said firstcircuit, said coupling member being mounted to and physically connectedsolely with said support member for movement relative to said first andsecond-mentioned members in response to the weight of said object, saidsecond circuit in response to said excitation signal and the position ofsaid coupling member producing at said junction an output signal havinga characteristic proportional to the position of said coupling memberand, therefore, indicative of the weight of said object.
 9. A device forsensing the weight of an object, comprising: a first circuit adapted forconnection with a signal producing source for producing an excitationsignal; a second circuit spaced from said first circuit and including anoutput junction; a support member adapted to support said object; acoupling member capacitively coupling said second circuit to said firstcircuit, said coupling member being mounted to and physically connectedsolely with said support member for movement in response to the weightof said object; said second circuit in response to said excitationsignal and the position of said coupling member producing at saidjunction an output signal having a characteristic proportional to theposition of said coupling member and, therefore, indicative of theweight of said object.